Editing Microfilament (section)

{{Short description|Filament in the cytoplasm of eukaryotic cells}}
[[Image:MEF microfilaments.jpg|thumb|Actin cytoskeleton of [[house mouse|mouse]] [[embryo]] [[fibroblast]]s, stained with [[Fluorescein isothiocyanate]]-[[phalloidin]]|250px]]

'''Microfilaments''', also called '''actin filaments''', are [[protein filament]]s in the [[cytoplasm]] of [[eukaryotic]] [[cell (biology)|cells]] that form part of the [[cytoskeleton]]. They are primarily composed of [[biopolymer|polymer]]s of [[actin]], but are modified by and interact with numerous other [[protein]]s in the cell. Microfilaments are usually about 7 [[Nanometre|nm]] in diameter and made up of two strands of actin. Microfilament functions include [[cytokinesis]], [[amoeboid movement]], [[Motility|cell motility]], changes in cell shape, [[endocytosis]] and [[exocytosis]], cell contractility, and mechanical stability. Microfilaments are flexible and relatively strong, resisting buckling by multi-piconewton compressive forces and filament fracture by nanonewton tensile forces.  In inducing [[Motility|cell motility]], one end of the actin filament elongates while the other end contracts, presumably by [[myosin II]] molecular motors.<ref name="Keith Roberts 2002">{{Cite book |last=Roberts |first=Keith |title=Molecular Biology of the Cell |last2=Raff |first2=Martin |last3=Alberts |first3=Bruce |last4=Walter |first4=Peter |last5=Lewis |first5=Julian |last6=Johnson |first6=Alexander |date=March 2002 |publisher=Routledge |isbn=0-8153-3218-1 |edition=4th |pages=1616 |name-list-style=vanc}}</ref> Additionally, they function as part of [[actomyosin]]-driven contractile molecular motors, wherein the thin filaments serve as tensile platforms for myosin's [[Adenosine triphosphate|ATP]]-dependent pulling action in [[muscle contraction]] and [[pseudopod]] advancement. Microfilaments have a tough, flexible framework which helps the cell in movement.<ref name="gunning">{{Cite journal |vauthors=Gunning PW, Ghoshdastider U, Whitaker S, Popp D, Robinson RC |date=June 2015 |title=The evolution of compositionally and functionally distinct actin filaments |journal=Journal of Cell Science |volume=128 |issue=11 |pages=2009–19 |doi=10.1242/jcs.165563 |pmid=25788699 |doi-access=free}}</ref>

Actin was first discovered in rabbit skeletal muscle in the mid 1940s by [[Brunó Ferenc Straub|F.B. Straub]].<ref>{{Cite journal |last=Kelpsch |first=Daniel J. |last2=Tootle |first2=Tina L. |date=December 2018 |title=Nuclear actin: from discovery to function |journal=Anatomical Record |volume=301 |issue=12 |pages=1999–2013 |doi=10.1002/ar.23959 |issn=1932-8486 |pmc=6289869 |pmid=30312531}}</ref> Almost 20 years later, [[Hugh Huxley|H.E. Huxley]] demonstrated that actin is essential for muscle constriction. The mechanism in which actin creates long filaments was first described in the mid 1980s. Later studies showed that actin has an important role in cell shape, motility, and cytokinesis.